1. Field of the Invention
Embodiments of the present invention generally relate to the field of semiconductor manufacturing processes and devices, and more particularly, to methods of depositing silicon-containing films to form semiconductor devices.
2. Description of the Related Art
As smaller transistors are manufactured, source/drain regions for sub-100 nm complementary metal-oxide semiconductor (CMOS) devices, such as silicon-containing metal oxide semiconductor field effect transistor (MOSFET) devices, are becoming more challenging to produce. Such MOSFET transistors may include p-channel MOS transistors, and n-channel MOS transistors. The PMOS transistor has a p-type source/drain region separated by an n-type channel (e.g., holes are responsible for conduction in the channel between the source/drain regions). The NMOS transistor has an n-type source/drain region separated by a p-type channel (e.g., electrons are responsible for conduction in the channel between the source/drain regions).
In NMOS applications, a source/drain region may be formed by etching a silicon substrate to make a recess that may be filled with a selectively grown silicon-carbon layer. The silicon-carbon layer is then doped with a dopant element to form the n-type source/drain region. In some embodiments, the silicon-carbon layer may also be used to increase the tensile strain in the channel of an NMOS transistor device (e.g., the mismatch of lattice constants between silicon and the SiC material generates a tensile stress which may be transferred in the lateral dimension to create tensile strain in channel of an NMOS device). The increased tensile strain improves the mobility of electrons in the channel of the device.
However, the silicon-carbon layer cannot be easily doped with dopant elements and retains a high percentage of carbon in the silicon-carbon film. Specifically, the diffusion of the dopant in the silicon-carbon layer is significantly retarded by the presence of carbon atoms at the substitutional lattice sites, which undesirably results in increased junction resistivity in the device (thereby offsetting the effect of the increased strain). Furthermore, doping of silicon-carbon with the dopant element significantly decreases the percentage of carbon in the doped silicon-carbon layer, which undesirably reduces the strain, and the electron mobility, in the channel of the NMOS device.
Thus, there is a need for improved methods for fabricating source/drain regions of NMOS transistor devices.